223 and 8208 XBR Load Opinion

[Doom]

I am looking for some experienced guidance. I have a load that I worked up using Newberry's OCW for a 223 Rem R700 Varmint which is quite accurate at 100 and 200 yds. Because I am limited to 300yds I have never chronographed the load. The load is 53 gr SMK with 25.5 grains 8208XBR, Lapua brass, Rem 7-1/2 primer and COAL of 2.250". Yesterday I shot at 100, 200, and 300 yds and recorded the required clicks (0.135"/click actual). Based on JBM (using its BC's) and the drop information I come up with a velocity of ~2950 fps. Hodgdon lists 25.4gr as max with 2.200" COAL and a velocity of 3310 fps. Sierra is 25.4gr with a COAL of 2.210 and 3250 fps.

I was surprised that this worked out to be such a low velocity. I realize that the longer COAL will drop pressure and velocity but is this what is going on here?

I have chronographed 55NBT with 25.1 grs 8208, Lapua Brass at 3050 fps years ago.

 

[spife7980]

Getting a real velocity is much better than trying to interpolate between two dissimilar sources to try and guess where you are at.

 

[Doom]

Getting a real velocity is much better than trying to interpolate between two dissimilar sources to try and guess where you are at.

I agree. However, I verified the scope click value last week (Nikon Monarch to verify if it was in/100yd or MOA and appears to be MOA). It took 36 clicks at 300 yds which is a drop of 14.6". Ultimately targets don't lie!

The scope check was 48 clicks at 100yds equaled 6.5" center to center.

 

[spife7980]

All of this extra math isnt really helping you find any answers is it?

 

[Doom]

No, and thats not the point. i’ve got a max load with > 4.5 MOA drop @ 300yds that should probably more like 3.5 to 3.8 if you believe the reloading data. I’ve never been that far off on this rifle or my 308. But I’ve never been .030 to .040” off of reloading data in 223.

 

[supercorndogs]

I have 3565 down for 25.8 of 8208 with a 53 v max in LC brass, from a factory 700 26" 1 in 9. My chromo is broken, so I can't reconfirm that, it seems really fast, but it would have come from my magneto speed. 3 MIL in a prairie dog town puts me, at what i
would guess is about 500y. I have never confirmed the dope in calculator on it. When I get to my ammo cabinet, I can a a coal.

 

[LawnMM]

Till you buy a chronograph it's all supposition. All this reverse engineering drop from scope clicks for finding muzzle velocity is dumb.

Why don't you hang a tall sheet of poster board and shoot at it with the scope on zero and measure actual drop from point of aim to point of impact.

That at least takes the scope variable out of the equation.

Or buy a fuckin chronograph. Magneto Sporters are like $180.

 

[spife7980]

No, and thats not the point.

That is the point. All your extra work hasnt gotten you one single answer has it?

 

[Doom]

I have 3565 down for 25.8 of 8208 with a 53 v max in LC brass, from a factory 700 26" 1 in 9. My chromo is broken, so I can't reconfirm that, it seems really fast, but it would have come from my magneto speed. 3 MIL in a prairie dog town puts me, at what i
would guess is about 500y. I have never confirmed the dope in calculator on it. When I get to my ammo cabinet, I can a a coal.

Thank you for a trying to answer my question.

 

[LawnMM]

Your dope is off because your muzzle velocity is incorrect, that's the answer to your question.

The solution to the problem is a chronograph, not how fast somebody else's gun fires a similar bullet and charge weight.

 

[sierracharlie338]

I run XBR in my 223 bolt gun with lapua brass and 69smks. I am at max book load and it is considerably slower than it’s “supposed to be”. Had to work up well above book max to find a load with acceptable velocity.

 

[Doom]

I run XBR in my 223 bolt gun with lapua brass and 69smks. I am at max book load and it is considerably slower than it’s “supposed to be”. Had to work up well above book max to find a load with acceptable velocity.

Do you remember the source of the data?

 

[sierracharlie338]

No but I can check my data for you later

Do you remember the source of the data?

 

[Doc68]

Do you remember the source of the data?

And book load is going to be low. That's so they can CYA, so yes you will be above book load most of the time.

 

[Doom]

Your dope is off because your muzzle velocity is incorrect, that's the answer to your question.

The solution to the problem is a chronograph, not how fast somebody else's gun fires a similar bullet and charge weight.

My dope is my dope, it is not off. In this case the dope for 300yds is 4.5 MOA (Indicated, note that on my scope, each 1/8 click is about 3% more than 1/8MOA). That is a heck of a drop for a 300yd 223 round. No chronograph data is going to change that. The question to other readers was experience with 8208, maximum loads and that particular bullet. In addition I have not played with large changes in COAL in 223 to observe what affect a 20 to 30 thousandth change in seating depth might have on pressure/velocity.

Any ballistic calculator must be trued to the actual dope to be useful. That is typically done by adjusting the Muzzle velocity or the ballistic coefficient, or a combination of those based on range. Some people actually use custom drag curves when working at extreme long range. I have chronographed rounds and found that typically the chronographed velocity and adjusting it +/-50 fps will closely match my dope at ranges out to 300yds, without modifying the BC. This is typical because the published ballistic coefficients at high supersonic speeds are usually the most accurate and follow the drag models well over the narrow range of velocities.

Unfortunately my chronograph is optical and on the day in question it was cloudy and hence not reliable. However it also meant that mirage was not an issue.

 

[LawnMM]

I rephrase and speak slower. The reason you're needing more adjustment than expected (actual drop not matching expected, dope not correct) is because your muzzle velocity isn't what you think it is. It's slower. That's why you need more than what you expected to need to hit at 300.

This is why we use a chronograph, so we can avoid the guesswork.

You only true up a calculator after you have all the variables, not the least of which is muzzle velocity.

There are people using custom drag curves a lot closer than ELR distances because they need less truing and tinkering to work. In my experience, they're dead nuts out to 1500.

The Chronograph isn't going to change what your current load uses to get to 300, but it WILL tell you WHY it's taking 4.5moa to get to 300.

As an example, if the muzzle velocity is what you think it is, that points to scope tracking error. If the muzzle velocity is lower than you think, it explains the extra drop.

 

[Doom]

LawnMM,

Since this is only a 223 300yd load I've not found it necessary to chronograph the load , at least with boat tail bullets like the NBT and 55gr FMJ. Just adjust the velocity and on those the velocity for Chrony and Dope usually match up pretty well.

I do chronograph all my 308 loads. Its a R700 so the lands reside in a different zip code than the chamber so any comparison between published velocity/charge weight is worthless.

I guess I'm going to have to invest in a MS but I can't use the sporter because of the brake on the 308. At our range we installed new baffles and combined with the shelter covers we don't have much time during the day where we have good light for an optical chronograph.

By the way, threw in scope data because I figured that question would come up.

 

[LawnMM]

Since this is only a 223 300yd load I've not found it necessary to chronograph the load , at least with boat tail bullets like the NBT and 55gr FMJ

You can't have it both ways. If you just want to load, shoot, and walk shots in at 300 that's fine.

But then you can't jump on here and complain it's taking 4.5moa instead of what you want it to take and ask why.